The 14 passengers were taken to Khoo Teck Puat Hospital in three ambulances, said a Singapore Civil Defence Force spokesman.

The bus drivers were not injured.

Six passengers said the bus in front, service 854, had suddenly jammed on its brakes after it left the bus stop.

But the driver of the bus behind, service 858, failed to react in time and ploughed into the rear of bus service 854.

The resulting crash sounded like "a big explosion", said a 63-year-old passenger on bus service 854, who wanted to be known only as Madam Lim.

THROWN

She said: "All of a sudden, there was a loud bang. It felt like a bomb and the next thing I knew, I was thrown forward.

"Thankfully, I wasn't injured as I sat further in front. No one was standing (in the bus) at the time."

Mr Kok Nee Cheong, 70, a retiree who was seated behind Madam Lim, said a woman was trying to stop the bus just as it was moving off.

"The driver saw her and suddenly stopped. If he had kept on going, this wouldn't have happened," said Mr Kok.

He said the sudden jolt left him with pain on his left shoulder and kneecaps.

The passengers immediately alighted. Some were angry and tried to find out the cause of the accident from the bus drivers.

Said Mr Kok: "Because our injuries were not that severe, some of us wanted to leave.

"But the drivers were quite concerned and told us to go to the hospital just in case."

Some of the other passengers had wounds and bruises on their limbs, while several complained of pain caused by hitting the neck rests of the seats in front or behind them.

Mr Lazarus Zachariah Bernard Ong, 40, was seated near the front of bus service 858 and suffered abrasions on his shins.

"The impact was very great. There were people crying, but other than that, all was okay," he said.

SMRT's vice-president of corporate information and communication Patrick Nathan said the company is looking into the incident.

He said: "We apologise for the accident. We're doing our best to get in touch with all 14 injured passengers and will render assistance as best we can."

Police investigations are ongoing.

Recent accidents involving public buses

Jan 11, 2016: Five people were injured in an accident involving a truck and an SMRT bus at Mandai Avenue near Mandai Crematorium. They suffered minor injuries and were sent conscious to Khoo Teck Puat Hospital.

July 21, 2015: Seven passengers were injured when SBS Transit bus service 238 crashed into a traffic light at the junction of Toa Payoh East and Toa Payoh Lorong 7. The Singapore Civil Defence Force sent two ambulances that took four women and three men to Tan Tock Seng Hospital. The bus was carrying about 30 passengers at the time.

June 4, 2015: 28 people were injured in an accident along Changi Road. It involved SMRT bus service 67 and two SBS Transit buses, services 2 and 7. They were travelling in the same direction when they collided. The injured people were taken to Changi General Hospital. It is understood that there were no serious injuries.